Solar cells, which convert sunlight into clean electric energy, have attracted attention for their environmental friendliness. Examples of known solar cells include silicon solar cells, which contain silicon such as monocrystalline silicon and polycrystalline silicon, and organic solar cells, which contain, for example, organic dyes or polymers to produce electromotive force. These solar cells are incapable of providing stable electric power because they cannot generate electricity at night or on cloudy days. For this reason, methods of using the solar cells in combination with secondary batteries have been studied in order to provide stable electric power.
For example, an energy storage dye-sensitized solar cell with a secondary battery function has been developed by utilizing the properties of dye-sensitized solar cells that the electricity generation is accompanied by an oxidation-reduction reaction (see Patent Literature 1, for example).
The Patent Literature 1 discloses a solar cell in which: an iodine electrolyte and an electrolyte containing lithium perchlorate are separated from each other by a cation exchange membrane; a photoanode, which is a porous electrode on which sensitized dyes are adsorbed, and a mesh counter electrode facing the photoanode are present in the iodine electrolyte; and a charge storage electrode is present in the electrolyte containing the lithium perchlorate.